Purifying raw indigo.



. UNITED STATES I PATENT OFFICE.

BENNO" HOMOLKA, OF FRANKFORT-ON-THE-MAIN, GERMANY, ASSIGNOR TOFARBWERKE, VORM.MEISTER, LUOIUS '& BRUNING, OF HOCHST- ON-THE-MAIN,GERMANY, A CORPORATION OF GERMANY.

PURIFYING RAW INDIGO.

SPECIFICATION formingpart of Letters Patent No. 702,730, dated June 17,1902.

, Application filed October 16, 1901. Serial No. 78,686, (No specimens.)

To all whom it may concern:

Be it known that I, BENNoHoMoLKA, Ph. D. a citizen of the Empire ofGermany, residing at Frankfort-on-the-Main, Germany, have inventedcertain new and useful Improvements in Purifying Raw Indigo, of whichthe following is a specification.

Raw indigo, especially such as is obtained after the process of K.Heumann, by heating phenylglycin, its homologues, and their carboxylicacids with caustic alkalies or by heating said bodies with alkali-amids,always contains a not inconsiderable quantity of brownred to red coloredby-products. Some of these are readilysoluble in dilute mineral acids,as well as in the usual solvents, (alcohol, acetone, &c.,) andconsequently may easily be eliminated. The others,however,obstinatelyresist all solvents coming into practical consideration, and thereforecannot be separated from the raw indigo, thus causing difficulties indyeing with the latter.

My process is based on the hitherto-unknown fact that the accessoryproducts of raw natural indigo as well as of raw artificial indigo arereadily soluble in pyridin and its homologues, which may be eliminatedby extracting raw indigo with pyridin bases.

The pyridin bases practically to be considered are those obtained fromcoal-tar, slatetar, brown coal-tar, and bone-oil after known methodsand, if necessary,purified by distillation.

The practical carrying outof the invention may be illustrated, forinstance, as follows:

Example: Into a suitably-arranged vessel provided with an agitator andstanding'in a water-bath (kept cool at first) are introduced fourhundred to five hundred kilos of the 40 above-named bases, to which areadded, with stirring, one hundred parts, by weight, of ground rawindigo. The water-bath is then heated to boiling-point and the indigoexposed for some hours to the action of the pyridin. The mass is thenfiltered in a filterpress and the indigo is washed in the press withfresh pyridin till it runs 01f no longer red, but colorless or feeblybluish. The indigo is then freed from pyridin by boiling it with waterand finally with dilute acids, then dried and put into marketablecondition.

Having now described my invention, what I claim is The herein-describedprocess of purifying raw indigo, which consists in extracting raw indigowith pyridin bases,'substantially as set forth.

. In testimony that I claim the foregoing as my invention I have signedmy name in pres- 6o ence of two subscribing witnesses.

BENNO HOMOLKA.

Witnesses:

ALFRED BRISBOIS, J OHANN HARTENSTEIN.

